Fluidized bed boilers recently have become of great interest as a very attractive means of generating heat. Many bubbling or turbulent fluidized bed boilers have proved to operate very satisfactory.
However, when it comes to fast fluidized bed boilers, serious problems have to be solved, particularly with regard to heat transfer, particle separation and control of operation.
Thus, the common use of cyclone particle separators means that the boiler has to be built from separated parts and cooling systems. Also, cyclone particle separators have very huge dimensions, at least at high boiler powers, giving serious lay-out problems.
Also, existing power control systems which primarily control fuel feed as the load varies, tend to be inacurate and to give so-called over shoot.
It is previously known that ordinary fluidized bed boilers can be provided with other particle separators than cyclone particle separators; cf. for instance GB A No. 2 046 886 which discloses a fluidized bed boiler having a baffle type separator located in the effluent gas pass. The amount of separated material is of course very low.
However, with regard to fast fluidized bed boilers, those skilled in the art have been convinced that particle separators of the cyclone type are necessary in view of the very large amount of particles to be separated and the high velocity of the gas-particle mixture.